You might have been offered courtesy vouchers versus the fare difference ($75 is a very exact number) so it merits a call to request the fare difference in addition to those vouchers. If you want to keep your seats in F and there is an earlier/later flight in the day that offers it (with seats open in the same cabin) you should be able to have it moved on a one-time basis at no charge. Good luck and post back with your results!

It would be helpful to know what the segment is and if the AA call was offering an actual fare difference refund or AA vouchers.